I’ve decided, after about a year of research, that the Raqia probably was solid after all. I believe this predominantly because of two verses:
Deep calls to deep at the roar of your waterfalls; all your breakers and your waves have gone over me.
See this excellent article for why I think this.
Secondly, 2 Samuel 22:8:
“Then the earth reeled and rocked; the foundations of the heavens trembled and quaked, because he was angry.
Whilst this is a poem, and we shouldn’t expect it to reflect science, speech of the supports of the heavens was hardly just poetry in the Ancient Near East. In Egypt, the air god Shu is described as supporting the sky, and in Mesopotamia, there are ‘bonds of heaven’, and Tiamat’s crotch holds up the heavens. I suspect then that David really did think there were foundations of heavens.
That said, I also think that the etymology of Raqia in no way necessitates a solid reading, though there is no reason why an ‘expanse’ ought to be non-solid.